Editas, cofounded by Harvard geneticist George Church, has set its sights initially on a rare eye disease called Leber congenital amaurosis, partly because scientists have identified the genetic defect but also because the eye is relatively easy to reach for a gene-editing procedure.

Intellia, which raised $108 million in its own IPO earlier this month, is developing treatments for cancer and liver disease.

More than $1 billion in venture capital financing has been plowed into gene-editing companies over the past two years, according to the Boston Consulting Group.

Larger biopharma companies also have been making big bets on the field. Boston’s Vertex Pharmaceuticals Inc. and Bayer AG of Germany have forged partnerships with CRISPR Therapeutics. Editas has an alliance with Juno Therapeutics Inc. of Seattle, while Intellia is collaborating with the Swiss drug giant Novartis AG, which bases its global research operation in Cambridge, and biotech Regeneron Pharmaceuticals Inc. of Tarrytown, New York.

Other companies, ranging from Sangamo BioSciences Inc. of Richmond, California, to France’s Cellectis, are working on different types of gene editing. But within the research field, CRISPR-Cas9 is considered the superior method and is being widely adopted worldwide.

CRISPR (clustered, regularly interspaced short palindromic repeats)/Cas9 (CRISPR-associated protein 9) and TALENs (transcription activator-like effector nucleases) comprise novel gene editing methods that overcome the challenges associated with previous technologies. Early published research on CRISPR/Cas9, coupled with a growing body of work on TALENs, suggests the potential to pursue therapeutic indications that have previously been intractable to traditional gene therapy, gene knock-down or other genome modification techniques. The CRISPR/Cas9 system, the most recent and exciting approach to emerge, acts by a mechanism in which the Cas9 protein binds to specific RNA molecules. The RNA molecules then guide the Cas9 complex to the exact location in the genome that requires repair. Similarly, TALENs are proteins that can be custom programmed to bind essentially any DNA sequence of interest and to direct gene modification activities to specific targets in the genome. CRISPR/Cas9 and TALENs uniquely enable highly efficient knock-out, knock-down or selective editing of defective genes in the context of their natural promoters, unlocking the ability to treat the root cause of a broad range of diseases.